Field of the Invention
The present invention relates to systems for determining the direction of incoming RF electromagnetic energy propagated through space from a remote RF source and, more particularly, to an RF direction finding system that uses a single RF receiver.
Direction finding or angle of arrival systems as they are known are measuring and indicating devices that have application in both military and commercial pursuits to locate remote RF sources. Electronic equipment of that type monitors the RF spectrum, which includes the microwave frequency range, for RF signals and determines the direction of the source of that signal: In military applications these signals may originate from a hostile radar transmitter and in commercial applications the RF signals may emanate from a directional marker or beacon signal transmitter. Specifics of those applications are known to those skilled in the art and need not be addressed in further detail in this application. Each system requires accurate measurement of the phase difference between the phase of signals received at two or more receiving antennas that are located physically spaced from one another. Given two ac signals that are sinusoidal in character and of the same frequency, the amplitude of the signals follow the mathematical expression Al=Ksin.OMEGA.t, where K represents the absolute value of the signals's amplitude, .OMEGA. the frequency, and t represents time. If the second signals amplitude is governed by the A2=Ksin(.OMEGA.wt+.THETA.), the factor .THETA. represents the phase difference between the two signals. Thus if .THETA. equals .THETA., the two signals are said to be "in-phase". Depending upon the direction of propagation of the incoming RF signal relative to the spatial positions of the antennas, the signal arrives at the two antennas slightly displaced in time. Consequently, the signal received at one antenna may be ever so slightly displaced in electrical phase relative to the phase of that same signal as it appears at the second antenna in the system. Since the signal emanates from a single source, this phase difference is thus representative of the angle at which the incoming signal traveled to the receiving station containing the direction finding equipment. In military application this direction information is considered together with other kinds of information provided by other electronic equipment, not relevant to the present invention, to enable personnel operating the direction finding equipment to determine the position of the hostile radar source.
Typical phase measurement systems in direction finding application incorporates two complete RF receivers which are phase matched and/or calibrated to provide the necessary reference and angle signals needed for accurate phase measurements. The RF receivers are complex and expensive pieces of electronic equipment. They must be checked and calibrated from time to time by skilled technicians to ensure that the receivers are properly "matched" so that accurate measurements are obtained. Such duplication of significant system elements, such as the RF receivers, is expensive.
A principal purpose of the present invention is to reduce the cost of manufacturing and maintaining RF direction finding equipment. A further object of the invention is to eliminate the need for a second RF receiver in RF direction equipment. An additional object is to provide direction finding apparatus that uses existing components and technology and that is of improved reliability resulting from elimination of complex elements typical of existing direction finding systems. A still further object is to provide a simplified method for determining the angle of arrival of an RF pulse signal.